Process for making metal ingots

ABSTRACT

A body of molten metal is provided in a lower portion of an ingot mold. A body of liquid slag is provided in said mold on top of said body of molten metal within a slag-confining wall. Heat energy is supplied to said body of liquid slag at a rate corresponding to at least 120 kilowatt-hours per metric ton of metal in said mold. The slag-confining wall is supplied on the outside thereof with a cooling fluid to cool said slag-confining wall sufficiently to maintain a layer of solid slag between said wall and said body of liquid slag. The molten metal in said mold is caused to solidify while those parts of said mold which are contacted by said metal are kept out of contact with cooling liquid.

United States Patent 1191 Plockinger et a1. Nov. 4, 1975 PROCESS FORMAKING METAL INGOTS 3,608,618 9/1971 Maskall 164/252 [75] Inventors:Erwin Plockinger; Gert Kuhnelt, I FOREIGN PATENTS OR APPLICATIONS bothof Kapfenberg, Ausma 1,237,115 6/1971 United Kingdom 164/50 [73]Assignee: Vereinigte Edelstahlwerke AG., OTHER PUBLICATIONS Vienna,Austria 30,000 Degrees with the Plasma Jet, Journal of [221 Flled 9,1973 Metals, 1959, January, 4042. [21] Appl. No.: 414,393 Potential ofElectroslag Refining, Metals, Mar.

Related US. Application Data 7' 44-48 [62] 1332;530:821 Ser. No.847,891, Aug.- 6, 1969, Pat. No. Primary Examiner Francis S. HusarAssistant Examiner-John E. Roethel [30] Foreign Application PriorityData Jan. 29, 1970 Austria 530/70 [57] ABSTRACT A body of molten metalis provided in a lower portion [52] US. Cl. 164/52 of an ingot mold, Abody of liquid slag is provided in [5l] Int. Cl. B221) 27/02 aid mold ontop of said body of molten metal within [58] Field Of Search 164/52, 48,50 a slag-confining wall, Heat energy is supplied to said body of liquidslag at a rate corresponding to at least [56] References Cited 120kilowatt-hours per metric. ton of metal in said UNITED STATES PATENTSmold. The slag-confining wallis supplied on the out- 2,191,479 2 1940Hopkins 164/52 Side there with a coding fluid to cool Said Slag2,248,623 7/1941 fl ki confining wall sufficiently to maintain a layerof solid 2,441,416 5 1943 Hopkin slag between said wall and said body ofliquid slag. 2,899,294 8/1959 Siemons.... The molten metal in said-rnold is caused to solidify 3,147,329 9/1964 Gage while those parts ofsaid mold which are contacted by 3,268,958 8/1966 sickbel't said metalare kept out of contact with cooling liquid. 3,271,828 9/1966 Shelton etal. 3,603,374 9/1971 Cooper 6 Claims, 2 Figures US. Patent Nov. 4, 1975Sheet 1 of2 3,916,978

US. Patent Nov. 4, 1975 Sheet 2 of2 3,916,978

FIG. 2

sist essentially of an ingot mold, which is closed at the bottom, andone or more fusible or non-fusible electrodes, which are adapted to belowered from above into said mold and may be connected to a source ofelectric current. When it is desired to make an ingot of steel, the moldmayconsist, e.g., of cast iron and may be cooled without need for aseparate liquid or gaseous cooling medium. In this case, the mold may befilled with molten steel, the free surface of which is covered by aliquid slag layer, and the top portion of the molten steel may be heatedas in crop end heating by a supply of electric current to the electrodeswhich are immersed in the liquid slag layer. As a result, the uppermostpart of the molten steel immediately below said slag will be heated andmaintained in a liquid state until a major part of the steel hasprogressively solidified attack by the slag and the molten steel andrequires a frequent renewal so that the maintenance costs are high.Besides, constituents of the refractory Iiningenter into solution andchange the chemical composition of the liquid slag which is in contactwith the lining; these constituents also contaminate the molten steel bythe formation of non-metallic inclusions as the steel solidifies. Ifthere is a supply of current and/orheat at a high rate through the slag,these disadvantages are so intensified that the lining is prematurelydestroyed within a. short time. For this reason, such known apparatusescan be used only where electric current and heat are supplied at lowrates, which are not sufficient for a thorough control of the structureof the ingot.

It is an object of the inventionto avoid said disadvantages by providingan improved apparatus, in which much higher currents at a rate of atleast 120 kilowatthours per metric ton of the weight of the solidifyingmolten steel can be supplied and the liquid slag cover and/or the moltensteel or other metal under said slag cover are subjected by said supplyor electric current or other energy to a high temperature rise in alarge cross-sectional area, whereas the erosion at the inside surfacesof the mold, particularly those which are contacted by the liquid slaglayer, is only small.

In an apparatus of the kind described hereinbefore, this object isaccomplished according to the invention in that the mold is not cooledwith liquid and is provided with a top part for receiving the liquidslag layer which floats on the molten steel, and said top part is cooledby a suitable fluid, e.g., a liquid. When the ingot mold of thisapparatus is filled with molten'steel and the top part is filled withthe liquid slag, that portion of the mostly metallic inside wall surfaceof the top part which confines the liquid slag is covered by asolidifiedslag layer becausesaid wall is cooled on the outside. As a result, thereis no direct contact between the very hot liquid slag and the insidewall of the top part, and there is no attack of the inside wall of thetop part by the slag and neither a chemical change of the slag nor acontamination of the molten steel takes place in the mold.

In another embodiment of the apparatus according to the invention, thetop ,part which serves to accommodate the liquid slag consists of adouble-walled hollow body, which may be made, e.g., of metal, and,ifvdesired, may be provided with internal guiding surfaces, and thespace between the outside and inside walls is provided with inlet andoutlet pipes for supplying and withdrawing the cooling liquid.

An embodiment of the invention will now be explained more fully and byway of example with reference to the drawing wherein; Y

FIG. 1 is a longitudinal sectional view of the apparatus of theinvention; and

FIG. 2 is a view similar to FIG. 1 wherein a conventional plasma torchfor use on the apparatus of the invention is illustrated. 7 i

The body 10 of themold consists, e.g., of cast-iron and is exposed onlyto the ambient atmosphere rather than cooled by a special .medium,suchas a liquid. A top part 20 is secured to the mold body and consistsof sheet metal elements, e.g., of steel or another material, which arejoined by welding. An annular distributing chamber 22 is attached to thetopedge of the top part 20 and contains a cooling liquid, such as water:The distributing chamber 22 is connectedto the liquid supply :coolingliquid. This trough communicates with the drain conduit-25.

The mold body-l0 rests on a bottom plate 40 and is sealed against thesame so that the mold body can be I filled to its top rim, e.g., withsteel, when'an ingot is'to be cast, without a leakage of steel'at thebottom joint. The top part 20 is in sealed engagement withthe' top edgeof the mold body so that premelted slag can be poured in over the levelof the molten steel. The walls of the top part are covered on the insidewith a layer 51 of solidified slag. Owing to the cooling on the 'outsideof the top part, this solidified slag cannot be melted even when theliquid slag layer is heated to a high temperature by a supply ofelectric current or other energy.

The solidified slag forms a solid separating layer between the liquidslag layer 50 and the wall.

One or more fusible electrodes 60 are disposed over the mold body 10 andadapted to be lowered into and lifted from the slag layer disposed overthe level of the molten steel. Two terminals of a source of alternatingcurrent are respectively connected to the electrode 60 and via thebottom plate 40 to the ingot 30 so that the circuit is closed by theslag layer 50 when the electrode is or the electrodes are immersed insaid slag layer. By resistance heating, the slag layer is maintained ata high temperature and heat is supplied to the ingot as it solidifies.The power source and all conductors of this circuit are dimensioned fora supply of energy of at least kilowatt-hours per metric ton of theweight of the ingot at a voltage of 30-100 volts. This supply of energyis required to ensure a high purity of the ingot and a dense,segregation-free structure in all portions of the ingot.

In another embodiment of the invention, which is not shown in thedrawing, one or more non-fusible electrodes are disposed over the moldbody and mold top part and adapted to be lifted and lowered. When theelectrodes are lowered into contact with the liquid slag, the circuitwill be closed so that the slag will be heated by resistance heating.Plasma torches or other energy sources may be used rather thancurrent-supplying electrodes to heat the slag cover. Such a conventionalplasma torch is illustrated in FIG. 2 and comprises a rod-shapedelectrode 81 and tubular counter-electrode 82 which surrounds theelectrode 81 and is open at its lower end. The tubular counter-electrode82 and is open at its lower end. The tubular counter-electrode 82 has aninlet pipe 83 through which an ionizable gas, such as argon, can beintroduced. An A.C. current source 84 is connected between electrodes81, 82. (The current source can also be a DC. current source.)

Steel ingots made with the aid of the apparatus according to theinvention have after solidification a good primary crystallization, aperfectly dense structure and a low content of non-metallic inclusionseverywhere. If the solidification rate is properly controlled, forinstance, the apparatus may be used to make ingots which are free of theknown V-segregation near the axis of the ingot.

If the mold is to be arranged in a pit or in an evacuated container, itis advantageous to provide the mold with a metallic top part consistingof a doublewalled hollow body, which may be provided in its interiorwith surface for guiding the liquid flowing through. In this case too,the top part may consist of welded sheet steel elements and the guidingsurfaces are preferably helical so that the cooling water flows aroundthe inside wall of the top part from bottom to top substantially along ahelix at an adequate velocity. The use of a doublewalled top partaffords the advantage that the draining of the cooling water does notdepend on a natural gradient but the conduits may be laid out asdesired, e.g., through the wall of the evacuated vessel.

Although the invention is illustrated and described with reference to aplurality of preferred embodiments thereof, it is to be expresslyunderstood that it is in no way limited to the disclosure of such aplurality of preferred embodiments, but is capable of numerousmodifications within the scope of the appended claims.

What is claimed is:

l. A process of making metal ingots in an ingot mold,

which comprises pouring molten metal in a lower portion of said mold,

pouring liquid slag into said mold on top of said body of molten metalwithin a slag confining wall,

supplying heating energy to said body of liquid slag at a ratecorresponding to at least kilowatthours per metric ton of metal in saidmold,

contacting the outside of said slagconfining wall with a cooling fluidto cool said slag-confining wall sufficiently to maintain a layer ofsolid slag between said wall and said body of liquid slag and causingsaid molten metal in said mold to solidify while maintaining theexterior wall surfaces of the walls of said mold opposite the interiorwall surfaces of said mold which are contacted by said metal out ofcontact with cooling liquid.

2. A process for producing ingots of nonalloyed or alloyed steel withimproved primary crystallization, re-

duced ingot segregation and reduced content of nonmetallic inclusions,comprising the steps of pouring molten steel into a mold;

placing a layer of liquid slag upon said molten steel in said mold;

supplying heat energy to said layer of liquid slag in said mold, saidheat energy being supplied at a rate of 120 kilowatt-hours per ton ofingot to be produced;

said layer of liquid slag being partially contained by side walls;

cooling said side walls and thereby producing a layer of solidified slagon the side of said side walls which is in contact with the slag; and

maintaining said layer of solidified slag on said side wall duringsolidification of molten steel in said mold.

3. The process for producing ingots of nonalloyed or alloyed steel asset forth in claim 2, wherein said layer of liquid slag is supplied withheat energy by passing an A.C. electric current through an electricresistance and conducting the heat energy thus produced to said layer ofliquid slag.

4. The process for producing ingots of non-alloyed or alloyed steel asset forth in claim 3, wherein said conduction of heat energy is effectedvia at least one nonfusible electrode.

5. The process as set forth in claim 3, wherein said conduction of heatenergy is effected via at least one fusible electrode.

6. The process as set forth in claim 3, wherein said 7 layer of liquidslag is supplied with heat energy via at least one plasma torch.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 9 97Dated November 4, 1975 Inventor(s) Erwin Ploeckinger et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the cover sheet Item (30) "January 29, 1970" has been changed to readJanuary 20, 1969 Signed and Sealed this twenty-fifth Day 'of May 1976[SEAL] Arrest:

RUI 'H C. MASON C. MARSHALL DANN Arresting Officer Commissioneruj'Palents and Tradvnmrks

1. A process of making metal ingots in an ingot mold, which comprisespouring molten metal in a lower portion of said mold, pouring liquidslag into said mold on top of said body of molten metal within a slagconfining wall, supplying heating energy to said body of liquid slag ata rate corresponding to at least 120 kilowatt-hours per metric ton ofmetal in said mold, contacting the outside of said slagconfining wallwith a cooling fluid to cool said slag-confining wall sufficientlY tomaintain a layer of solid slag between said wall and said body of liquidslag and causing said molten metal in said mold to solidify whilemaintaining the exterior wall surfaces of the walls of said moldopposite the interior wall surfaces of said mold which are contacted bysaid metal out of contact with cooling liquid.
 2. A process forproducing ingots of nonalloyed or alloyed steel with improved primarycrystallization, reduced ingot segregation and reduced content ofnonmetallic inclusions, comprising the steps of pouring molten steelinto a mold; placing a layer of liquid slag upon said molten steel insaid mold; supplying heat energy to said layer of liquid slag in saidmold, said heat energy being supplied at a rate of 120 kilowatt-hoursper ton of ingot to be produced; said layer of liquid slag beingpartially contained by side walls; cooling said side walls and therebyproducing a layer of solidified slag on the side of said side wallswhich is in contact with the slag; and maintaining said layer ofsolidified slag on said side wall during solidification of molten steelin said mold.
 3. The process for producing ingots of nonalloyed oralloyed steel as set forth in claim 13, wherein said layer of liquidslag is supplied with heat energy by passing an A.C. electric currentthrough an electric resistance and conducting the heat energy thusproduced to said layer of liquid slag.
 4. The process for producingingots of non-alloyed or alloyed steel as set forth in cliam 3, whereinsaid conduction of heat energy is effected via at least one non-fusibleelectrode.
 5. The process as set forth in claim 3, wherein saidconduction of heat energy is effected via at least one fusibleelectrode.
 6. The process as set forth in claim 3, wherein said layer ofliquid slag is supplied with heat energy via at least one plasma torch.